First off, realize "ping" is relative. Let me quantify that a little...
Although you may get 50ms to anandtech.com, I may get 125ms. But I may get 50ms to a different server (say
www.google.com) while you get 125ms.
Saying that, your first step is to run "traceroute". On MS systems the command is tracert <site>
This will tell you the route from you to the site.
Now, you can ping the first ip number returned, and that will be _your_ gateway. You definately want low values here consistantly. Idealy you should see below 30ms average. You probably won't have a chance of complaining even if it's 100ms average. If it is above that, there is definately a problem with the cable company overloading your area. The problem is that you will have to find a tech that not only understands you, but is willing to do something about it.
You can continue this process to the next router and the next to find were the problem lays.
Personally, my area is overloaded bad, but InsightBB thinks that as long as they can ping you, then everything is ok. Maybe someday I'll feel like spending a few hours on the phone tracking down a knowledgable person (during _their_ business hours) and get things fixed.
Hope this helps.